The present invention relates to the field of fluid compounding for preparing fluids particularly for the treatment of renal insufficiency. More specifically, it relates to an apparatus for the treatment of renal insufficiency configured for compounding finished fluids from two or more constituent fluids for use as a kidney dialyzing fluid.
In particular, the invention may be used for preparing fluids for peritoneal dialysis, particularly for preparing fluids on-site (e.g. at patient's home).
The kidneys fulfil many functions, including the removal of water, the excretion of catabolites (or waste from the metabolism, for example urea and creatinine), the regulation of the concentration of the electrolytes in the blood (e.g. sodium, potassium, magnesium, calcium, bicarbonate, phosphate, chloride) and the regulation of the acid/base equilibrium within the body, which is obtained in particular by the removal of weak acids (phosphates, monosodium acids) and by the production of ammonium salts.
In individuals who have lost the use of their kidneys, since these excretion and regulation mechanisms no longer work, the body accumulates water and waste from the metabolism and exhibits an excess of electrolytes, as well as, in general, acidosis, the pH of the blood plasma shifting downwards, below 7.35 (the blood pH normally varies within narrow limits of between 7.35 and 7.45).
In the treatment of patients suffering acute or chronic renal insufficiency, dialysis therapy is employed. The two general categories of dialysis therapy are hemodialysis and peritoneal dialysis.
In hemodialysis, the patient's blood is cleansed by passage through an artificial kidney in an extracorporeal membrane system.
The blood treatment involves extracorporeal circulation through an exchanger having a semipermeable membrane (dialyzer) in which the patient's blood is circulated on one side of the membrane and a dialysis liquid, comprising the main electrolytes of the blood in concentrations close to those in the blood of a healthy subject, is circulated on the other side.
Furthermore, a pressure difference is created between the two compartments of the dialyzer which are delimited by the semipermeable membrane, so that a fraction of the plasma fluid passes by ultrafiltration through the membrane into the compartment containing the dialysis liquid.
In peritoneal dialysis, dialyzing fluid is infused into the patient's peritoneal cavity. This cavity is lined by the peritoneal membrane which is highly vascularized. The metabolites are removed from the patient's blood by diffusion across the peritoneal membrane into the dialyzing fluid. Excess fluid, i.e. water is also removed by osmosis induced by a hypertonic dialyzing fluid.
When an aqueous solution is instilled into the peritoneal cavity, the solute composition equilibrates with that of plasma water by passive diffusion along electrochemical concentration gradients. In addition the flux of fluid across the peritoneum in response to an osmotic agent moves solutes in the absence of a concentration gradient, leading to the concept that solute transport occurs partly by convection or ‘solvent drag’. Removal of excess fluid is achieved by adding to the solution various concentrations of an osmotic agent (usually dextrose). Ultrafiltration continues until the dialysate becomes virtually isotonic, after which the rate that fluid is absorbed into the circulation exceeds that of the ultrafiltration induced by transcapillary hydrostatic pressure gradient alone. Net solute and water removal during peritoneal dialysis have been shown to be reduced by dialysate absorption. Through these two processes, diffusion and osmotic ultrafiltration, appropriate quantities of solute metabolites and fluid need to be removed to maintain the patient's body fluid volumes and composition within appropriate limits.
There are various types of peritoneal dialysis therapies, including continuous ambulatory peritoneal dialysis (“CAPD”), automated peritoneal dialysis (“APD”), including tidal flow APD, and continuous flow peritoneal dialysis (“CFPD”).
CAPD is a manual dialysis treatment. The patient connects manually an implanted catheter to a drain, allowing spent dialysate fluid to drain from the peritoneal cavity. The patient then connects the catheter to a bag of fresh dialyzing fluid, infusing fresh dialyzing fluid through the catheter and into the patient. The patient disconnects the catheter from the fresh dialyzing fluid bag and allows the dialyzing fluid to dwell within the peritoneal cavity, wherein the transfer of waste, toxins and excess water takes place. After a dwell period, the patient repeats the manual dialysis procedure, for example, four times per day, each treatment lasting about an hour. Manual peritoneal dialysis requires a significant amount of time and effort from the patient, leaving ample room for improvement.
Automated peritoneal dialysis (“APD”) is similar to CAPD in that the dialysis treatment includes drain, fill, and dwell cycles. APD machines, however, perform the cycles automatically, typically while the patient sleeps. APD machines free patients from having to manually perform the treatment cycles and from having to transport supplies during the day. APD machines connect fluidly to an implanted catheter, to a source or bag of fresh dialyzing fluid and to a fluid drain. APD machines pump fresh dialyzing fluid from the dialyzing fluid source, through the catheter, into the patient's peritoneal cavity and allow the dialyzing fluid to dwell within the cavity and the transfer of waste, toxins and excess water to take place. APD machines pump spent dialysate from the peritoneal cavity, through the catheter, to the drain. As with the manual process, several drain, fill and dwell cycles occur during APD. A “last fill” occurs often at the end of CAPD and APD, which remains in the peritoneal cavity of the patient until the next treatment.
Both CAPD and APD are batch type systems that send spent dialysis fluid to a drain. Tidal flow systems are modified batch systems. With tidal flow, instead of removing all the fluid from the patient over a longer period of time, a portion of the fluid is removed and replaced after smaller increments of time.
Continuous flow or CFPD systems clean or regenerate spent dialysate instead of discarding it. The systems flow fluid into or out of the patient, through a loop. Dialyzing fluid flows into the peritoneal cavity through one catheter lumen and out another catheter lumen. The fluid exiting the patient passes through a reconstitution device that removes waste from the dialysate, e.g., via a urea removal column that employs urease to enzymatically convert urea into ammonia. The ammonia is then removed from the dialysate by adsorption prior to reintroduction of the dialyzing fluid into the peritoneal cavity. CFPD systems are more complicated typically than batch systems.
CAPD, APD (including tidal flow) and CFPD systems can employ a pumping cassette. The pumping cassette typically includes a flexible membrane that is moved mechanically to push and pull dialysis fluid out of and into, respectively, the cassette.
Peritoneal dialysis requires the maintenance of aseptic technique for connection because of the high risk of peritoneal infection. The risk of infection is particularly high due to the high number of exchanges of dialyzing fluid which the patient is exposed to.
In one form of peritoneal dialysis, an automated cycler is used to infuse and drain dialyzing fluid. This form of treatment may be done automatically at night while the patient sleeps The cycler measures the amount of fluid infused and the amount removed to compute the net fluid removal. The treatment sequence usually begins with an initial drain cycle to empty the peritoneal cavity of spent dialysate. The cycler then performs a series of fill, dwell, and drain cycles, typically finishing with a fill cycle.
Peritoneal dialysis generally requires large volumes of dialyzing fluid. Generally, at each application, or exchange, a given patient will infuse 2 to 3 liters of dialyzing fluid into the peritoneal cavity. The fluid is allowed to dwell for approximately 1 to 3 hours, at which time it is drained out and exchanged for fresh fluid. Generally, four such exchanges are performed daily. Therefore, approximately 8 to 20 liters of dialyzing fluid is required per day, 7 days a week, 365 days a year for each patient.
Dialyzing fluids have traditionally been provided in sealed, heat sterilized form, ready for use. Peritoneal dialysis is typically performed using bags with three different concentration of dextrose. The bags are being delivered to a patient's home as 1 liter to 6 liter bags with different dextrose concentrations and a normal daily consumption is around 8 to 20 liters of fluid.
In light of above, several problems become apparent. Shipping and storage of the sheer volume of fluids required is space consuming. Additionally, the use of multiple prefilled bags produces waste materials in the form of empty containers and packaging.
An improved peritoneal dialysis system is needed accordingly.